1. Field of the Invention
The present invention relates to an interrogator circuit for a lock and, more particularly, to an interrogator-coil circuit integrated on a circuit board.
2. Description of Related Art
A simple lock-and-key arrangement in some circumstances is deemed insufficiently secure to protect valuable or dangerous items. Unauthorized persons with enough expertise can often open a lock by somehow duplicating the key. This is especially true for automobiles, in which a traditional key-lock ignition can be defeated by an experienced car thief. However, it is equally true for other items.
One approach to this problem has been to use an "interrogator" circuit, which in an automobile is incorporated into the ignition circuitry. The interrogator circuit, mounted in the vehicle, activates the ignition circuit to permit the vehicle engine to be started. The interrogator circuit has a decoder programmed to activate the ignition only when it receives from the key the particular coded signal preprogrammed into the interrogator for that vehicle. By matching the interrogator and the key, a different key, even one that fits the vehicle ignition lock, will not start the engine.
The system is implemented by providing an electromagnetic coil in the vehicle. The coil is typically a wire wound around a bezel surrounding the key opening in the vehicle ignition lock. The vehicle coil in the bezel cooperates with a corresponding coil embedded in the handle of the vehicle ignition key. When the ignition key is inserted into the ignition lock, the vehicle coil, which is always energized, is brought into proximity with a coil in the key handle to induce a current in it. The induced current in turn activates an RF transmitter in the key handle. The transmitter emits a signal with a signature (say a particular frequency) recognized by the interrogator circuit's decoder, and the interrogator circuit activates the ignition and starts the vehicle engine. This type of system requires no independent source of electrical power in the key.
This is a very effective approach, and has application beyond vehicle ignition locks. However, the mere fact that the system comprises multiple components makes it more expensive both to manufacture and install. As presently implemented the vehicle coil consists of copper wire wound on a spool in the bezel, which makes it expensive to manufacture. In addition, the interrogator circuit is typically located remote from the ignition lock, necessitating separate wiring for the different system components, adding further to the expense attributable to system installation.